Re: [RFC][PATCH] PCI, pciehp: make every slot have its own workqueue to avoid deadlock

[Yijing Wang <wangyijing@huawei.com>]

On 2012/10/31 17:20, Kaneshige, Kenji wrote:
> Let me confirm the problem. My understanding of the problem is below.
> Is my understanding correct?
> 

Yes，exactly.

> - Your hardware has nested PCIe hotplug slots like below.
> 
>     --<slot A>--<Slot B>
> 
> - Hot-removal request (attention button event) comes to <slot A>
> - Pciehp driver queue the hot-removal work
> - This hot-removal work try to remove <slot B>
> - To remove <slot B>, pciehp flush the pciehp_wq, but it never finishes
>   because hot-removal work is in progress. ===> deadlock
> 
> Regards,
> Kenji Kaneshige
> 
> 
> 
>> -----Original Message-----
>> From: Yijing Wang [mailto:wangyijing@huawei.com]
>> Sent: Wednesday, October 31, 2012 4:11 PM
>> To: Bjorn Helgaas; Yinghai Lu; Kaneshige, Kenji/金重 憲治; Rafael; Rusty
>> Russell; Mauro Carvalho Chehab; Oliver Neukum
>> Cc: linux-pci@vger.kernel.org; Hanjun Guo; jiang.liu@huawei.com; Yijing
>> Wang
>> Subject: [RFC][PATCH] PCI, pciehp: make every slot have its own workqueue
>> to avoid deadlock
>>
>> Currently, pciehp use global pciehp_wq to handle hotplug event from
>> hardware.
>> Hot remove path will be blocked if a hotplug slot connected a IO-BOX(composed
>> of PCIe
>> Switch and some slots which support hotplug, eg.PLX8696). The hot removed
>> work was queued
>> into pciehp_wq. But in the hot-remove path, pciehp driver would flush
>> pciehp_wq when
>> the pcie port(support pciehp) was removed. In this case the hot-remove path
>> blocked.
>> This patch remove the global pciehp_wq and create a new workqueue for every
>> slot to
>> avoid above problem.
>>
>> -+-[0000:40]-+-00.0-[0000:41]--
>>  |           +-01.0-[0000:42]--+-00.0  Intel Corporation 82576 Gigabit
>> Network Connection
>>  |           |                 \-00.1  Intel Corporation 82576 Gigabit
>> Network Connection
>>  |           +-03.0-[0000:43]----00.0  LSI Logic / Symbios Logic
>> SAS1064ET PCI-Express Fusion-MPT SAS
>>  |           +-04.0-[0000:44]--
>>  |           +-05.0-[0000:45]--
>>  |
>> +-07.0-[0000:46-4f]----00.0-[0000:47-4f]--+-04.0-[0000:48-49]----00.0-
>> [0000:49]--
>>  |           |(hotplug slot)
>> +-08.0-[0000:4a]--
>>  |           |
>> +-09.0-[0000:4b]--
>>  |           |
>> +-10.0-[0000:4c]--
>>  |           |
>> +-11.0-[0000:4d]--
>>  |           |
>> +-14.0-[0000:4e]--
>>  |           |
>> \-15.0-[0000:4f]--+-00.0  Intel Corporation 82576 Gigabit Network
>> Connection
>>  |           |                                         (hotplug slot)
>> \-00.1  Intel Corporation 82576 Gigabit Network Connection
>>
>>
>> Signed-off-by: Yijing Wang <wangyijing@huawei.com>
>> ---
>>  drivers/pci/hotplug/pciehp.h      |    2 +-
>>  drivers/pci/hotplug/pciehp_core.c |   11 ++---------
>>  drivers/pci/hotplug/pciehp_ctrl.c |    8 ++++----
>>  drivers/pci/hotplug/pciehp_hpc.c  |   14 ++++++++++++--
>>  4 files changed, 19 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
>> index 26ffd3e..2c113de 100644
>> --- a/drivers/pci/hotplug/pciehp.h
>> +++ b/drivers/pci/hotplug/pciehp.h
>> @@ -44,7 +44,6 @@ extern bool pciehp_poll_mode;
>>  extern int pciehp_poll_time;
>>  extern bool pciehp_debug;
>>  extern bool pciehp_force;
>> -extern struct workqueue_struct *pciehp_wq;
>>
>>  #define dbg(format, arg...)
>> 	\
>>  do {
>> 	\
>> @@ -78,6 +77,7 @@ struct slot {
>>  	struct hotplug_slot *hotplug_slot;
>>  	struct delayed_work work;	/* work for button event */
>>  	struct mutex lock;
>> +	struct workqueue_struct *wq;
>>  };
>>
>>  struct event_info {
>> diff --git a/drivers/pci/hotplug/pciehp_core.c
>> b/drivers/pci/hotplug/pciehp_core.c
>> index 916bf4f..0914211 100644
>> --- a/drivers/pci/hotplug/pciehp_core.c
>> +++ b/drivers/pci/hotplug/pciehp_core.c
>> @@ -42,7 +42,6 @@ bool pciehp_debug;
>>  bool pciehp_poll_mode;
>>  int pciehp_poll_time;
>>  bool pciehp_force;
>> -struct workqueue_struct *pciehp_wq;
>>
>>  #define DRIVER_VERSION	"0.4"
>>  #define DRIVER_AUTHOR	"Dan Zink <dan.zink@compaq.com>, Greg
>> Kroah-Hartman <greg@kroah.com>, Dely Sy <dely.l.sy@intel.com>"
>> @@ -340,18 +339,13 @@ static int __init pcied_init(void)
>>  {
>>  	int retval = 0;
>>
>> -	pciehp_wq = alloc_workqueue("pciehp", 0, 0);
>> -	if (!pciehp_wq)
>> -		return -ENOMEM;
>> -
>>  	pciehp_firmware_init();
>>  	retval = pcie_port_service_register(&hpdriver_portdrv);
>>   	dbg("pcie_port_service_register = %d\n", retval);
>>    	info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
>> - 	if (retval) {
>> -		destroy_workqueue(pciehp_wq);
>> +	if (retval)
>>  		dbg("Failure to register service\n");
>> -	}
>> +
>>  	return retval;
>>  }
>>
>> @@ -359,7 +353,6 @@ static void __exit pcied_cleanup(void)
>>  {
>>  	dbg("unload_pciehpd()\n");
>>  	pcie_port_service_unregister(&hpdriver_portdrv);
>> -	destroy_workqueue(pciehp_wq);
>>  	info(DRIVER_DESC " version: " DRIVER_VERSION " unloaded\n");
>>  }
>>
>> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c
>> b/drivers/pci/hotplug/pciehp_ctrl.c
>> index 27f4429..38f0186 100644
>> --- a/drivers/pci/hotplug/pciehp_ctrl.c
>> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
>> @@ -49,7 +49,7 @@ static int queue_interrupt_event(struct slot *p_slot,
>> u32 event_type)
>>  	info->p_slot = p_slot;
>>  	INIT_WORK(&info->work, interrupt_event_handler);
>>
>> -	queue_work(pciehp_wq, &info->work);
>> +	queue_work(p_slot->wq, &info->work);
>>
>>  	return 0;
>>  }
>> @@ -344,7 +344,7 @@ void pciehp_queue_pushbutton_work(struct work_struct
>> *work)
>>  		kfree(info);
>>  		goto out;
>>  	}
>> -	queue_work(pciehp_wq, &info->work);
>> +	queue_work(p_slot->wq, &info->work);
>>   out:
>>  	mutex_unlock(&p_slot->lock);
>>  }
>> @@ -377,7 +377,7 @@ static void handle_button_press_event(struct slot
>> *p_slot)
>>  		if (ATTN_LED(ctrl))
>>  			pciehp_set_attention_status(p_slot, 0);
>>
>> -		queue_delayed_work(pciehp_wq, &p_slot->work, 5*HZ);
>> +		queue_delayed_work(p_slot->wq, &p_slot->work, 5*HZ);
>>  		break;
>>  	case BLINKINGOFF_STATE:
>>  	case BLINKINGON_STATE:
>> @@ -439,7 +439,7 @@ static void handle_surprise_event(struct slot *p_slot)
>>  	else
>>  		p_slot->state = POWERON_STATE;
>>
>> -	queue_work(pciehp_wq, &info->work);
>> +	queue_work(p_slot->wq, &info->work);
>>  }
>>
>>  static void interrupt_event_handler(struct work_struct *work)
>> diff --git a/drivers/pci/hotplug/pciehp_hpc.c
>> b/drivers/pci/hotplug/pciehp_hpc.c
>> index 13b2eaf..8e5e571 100644
>> --- a/drivers/pci/hotplug/pciehp_hpc.c
>> +++ b/drivers/pci/hotplug/pciehp_hpc.c
>> @@ -773,23 +773,33 @@ static void pcie_shutdown_notification(struct
>> controller *ctrl)
>>  static int pcie_init_slot(struct controller *ctrl)
>>  {
>>  	struct slot *slot;
>> +	char name[32];
>>
>>  	slot = kzalloc(sizeof(*slot), GFP_KERNEL);
>>  	if (!slot)
>>  		return -ENOMEM;
>> -
>> +
>> +	snprintf(name, sizeof(name), "pciehpd_%s",
>> +		pci_name(ctrl->pcie->port));
>> +	slot->wq = create_singlethread_workqueue(name);
>> +	if (!slot->wq)
>> +		goto abort;
>>  	slot->ctrl = ctrl;
>>  	mutex_init(&slot->lock);
>>  	INIT_DELAYED_WORK(&slot->work, pciehp_queue_pushbutton_work);
>>  	ctrl->slot = slot;
>>  	return 0;
>> +abort:
>> +	kfree(slot);
>> +	return -1;
>>  }
>>
>>  static void pcie_cleanup_slot(struct controller *ctrl)
>>  {
>>  	struct slot *slot = ctrl->slot;
>>  	cancel_delayed_work(&slot->work);
>> -	flush_workqueue(pciehp_wq);
>> +	flush_workqueue(slot->wq);
>> +	destroy_workqueue(slot->wq);
>>  	kfree(slot);
>>  }
>>
>> --
>> 1.7.1
>>
> 
> 
> .
> 


-- 
Thanks!
Yijing